Nanoscale Confinement and Fluorescence Effects of Bacterial Light Harvesting Complex LH2 in Mesoporous Silicas (original) (raw)
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Behavior of fluorescent molecules bound to the interior of silica nanocapsules in various solvents
Journal of Colloid and Interface Science, 2009
Porous silica nanocapsules with 20% 3-aminopropyltrimethoxysilane (APS)-bound 6-carboxy-fluorescein (APS-fluorescein) and 80% APS molecules adsorbed on the surface of a 50-nm-diameter Au core were prepared by a modified core-shell method. Silica mesoporous nanocapsules were obtained after the Au cores were dissolved in sodium cyanide. The size of the pores in the silica shells corresponded to the area of the fluorescein (approximately 1.02 nm 2 ) in each APS-fluorescein molecule, which was bound to the silica shell by coupling between the silanol groups of APS in the APS-fluorescein molecule and the silica shell. The amino group of APS bound to the silica inside the shell is also reactive. Dy485XL N-hydroxysuccinimide ester (NHS) molecules were then added to the mesoporous silica nanocapsules in the solution and bonded to the amino group of the interior. Thus, mesoporous (fluorescein and Dy485XL)-bound silica nanocapsules were obtained. The fluorescence of Dy485XL was only observed in the mesoporous (fluorescein and Dy485XL)-bound silica nanocapsules in aqueous solution after ultrafiltration. However, the fluorescence of fluorescein reappeared after the addition of acetonitrile. Furthermore, upon adding various solvents to the mesoporous (fluorescein and Dy485XL)-bound silica nanocapsules, their fluorescence varied with that of fluorescein or Dy485XL. In the case of a mixture of 6-carboxy-fluorescein-N-hydroxysuccinimide (FLUOS) and Dy485XL-NHS free molecules in aqueous solution, the fluorescence of FLUOS was observed. Such different fluorescence phenomena demonstrated that Dy485XL-NHS molecules can easily penetrate into the nanocapsule interior via the pores and that the interior of the silica nanocapsules can bind to Dy485XL molecules. These fluorescence behaviors are discussed in terms of fluorescence resonance energy transfer (FRET) and solvatochromism.
Mapping the Distribution of an Individual Chromophore Interacting with Silica-Based Nanomaterials
Journal of the American Chemical Society, 2010
Exploring the interactions of molecules with silica-based mesoporous and nanoparticle materials at the atomic level and understanding of the forces that govern such H-bonds and electrostatic interactions are of fundamental importance to nanocatalysis, nanomedicine, and nanophotonics. In our approach, we studied in single-molecule time and spectral domains a proton-transfer chromophore complexed (by diffusion) and covalently bonded to MCM-41 mesoporous nanomaterial and silica particles. The results reveal strong dependence of the distribution and behavior of the interacting single molecule with the nanopores on the mode of sample preparation and nature of the involved interaction. The change at the single molecule level results in an up to 126 nm (∼4650 cm-1) spectral shift (from 462 to 588 nm) and almost two times longer lifetime. Furthermore, a change in the electronic charges of the mesoporous framework results in significant narrowing in the emission band of the guest. The results are explained in terms of electronic nanoconfinement but at a single-molecular level.
The journal of physical chemistry. B, 2015
Manipulating the photophysical properties of light-absorbing units is a crucial element in the design of biomimetic light-harvesting systems. Using a highly tunable synthetic platform combined with transient absorption and time-resolved fluorescence measurements and molecular dynamics simulations, we interrogate isolated chromophores covalently linked to different positions in the interior of the hydrated nanoscale cavity of a supramolecular protein assembly. We find that, following photoexcitation, the time scales over which these chromophores are solvated, undergo conformational rearrangements, and return to the ground state are highly sensitive to their position within this cavity and are significantly slower than in a bulk aqueous solution. Molecular dynamics simulations reveal the hindered translations and rotations of water molecules within the protein cavity with spatial specificity. The results presented herein show that fully hydrated nanoscale protein cavities are a promis...
Photosynthetic Electron Transfer from Reaction Center Pigment−Protein Complex in Silica Nanopores
Langmuir, 2010
A photosynthetic reaction center (RC) pigment-protein complex purified from a thermophilic purple photosynthetic bacterium, Thermochromatium tepidum, was adsorbed to a folded-sheet silica mesoporous material (FSM). The RC has a molecular structure with a 7.0 Â 5.0 Â 13 nm diameter. The amount of RC adsorbed to the FSM compound with an average internal pore diameter of 7.9 nm (FSM 7.9 ) was high at 0.29 gRC/gFSM, while that to the FSM 2.7 (2.7 nm diameter) was low at 0.02 gRC/gFSM, suggesting the specific binding of the RC into the 7.9 nm pores of FSM 7.9 . An N 2adsorption isotherm study indicated the incorporation of the RC into the 7.9 nm pores. The RC inside FSM 7.9 showed absorption spectra in the visible and infrared regions similar to those of the RC in solution, indicating almost no structural changes induced by the adsorption. The RC-FSM 7.9 conjugate showed the high photochemical activity with the increased thermal stability up to 50°C in the measurements by laser spectroscopy. The conjugates rapidly provided electrons to a dye in the outer medium or showed electric current on the ITO electrode upon the illumination. The RC-FSM conjugate will be useful for the construction of artificial photosynthetic systems and new photodevices.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2012
Integral membrane proteins constitute more than third of the total number of proteins present in organisms. Solubilization with mild detergents is a common technique to study the structure, dynamics, and catalytic activity of these proteins in purified form. However beneficial the use of detergents may be for protein extraction, the membrane proteins are often denatured by detergent solubilization as a result of native lipid membrane interactions having been modified. Versatile investigations of the properties of membraneembedded and detergent-isolated proteins are, therefore, required to evaluate the consequences of the solubilization procedure. Herein, the spectroscopic and kinetic fingerprints have been established that distinguish excitons in individual detergent-solubilized LH2 light-harvesting pigment-protein complexes from them in the membrane-embedded complexes of purple photosynthetic bacteria Rhodobacter sphaeroides. A wide arsenal of spectroscopic techniques in visible optical range that include conventional broadband absorption-fluorescence, fluorescence anisotropy excitation, spectrally selective hole burning and fluorescence line-narrowing, and transient absorption-fluorescence have been applied over broad temperature range between physiological and liquid He temperatures. Significant changes in energetics and dynamics of the antenna excitons upon self-assembly of the proteins into intracytoplasmic membranes are observed, analyzed, and discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.
Langmuir, 2008
We describe here a method for study of bulk release and local molecular transport within mesoporous silica spheres. We have analyzed the loading and release of charged fluorescent dyes from monodisperse mesoporous silica (MMS) spheres with an average pore size of 2.7 nm. Two different fluorescent dyes, one cationic and one anionic, have been loaded into the negatively charged porous material and both the bulk release and the local molecular transport within the MMS spheres have been quantified by confocal laser scanning microscopy. Analysis of the time-dependent release and the concentration profiles of the anionic dye within the spheres show that the spheres are homogeneous and that the release of this nonadsorbing dye follows a simple diffusion-driven process. The concentration of the cationic dye varies radially within the MMS spheres after loading; there is a significantly higher concentration of the dye close to the surface of the spheres (forming a "skin") compared to that at the core. The release of the cationic dye is controlled by diffusion after an initial period of rapid release. The transport of the cationic dye within the MMS spheres of the dye from the core to near the surface is significantly faster compared to the transport within the surface "skin". A significant fraction of the cationic dye remains permanently attached to the negatively charged walls of the MMS spheres, preferentially near the surface of the spheres. Relating bulk release to the local molecular transport within the porous materials provides an important step toward the design of new concepts in controlled drug delivery and chromatography.
Probing biological light-harvesting phenomena by optical cavities
Physical Review B, 2012
We propose a driven optical cavity quantum electrodynamics (QED) set up aimed at directly probing energy transport dynamics in photosynthetic biomolecules. We show that detailed information concerning energy transfer paths and delocalization of exciton states can be inferred (and exciton energies estimated) from the statistical properties of the emitted photons. This approach provides us with a novel spectroscopic tool for the interrogation of biological systems in terms of quantum optical phenomena which have been usually studied for atomic or solid-state systems, e.g. trapped atoms and semiconductor quantum dots.
Biophysical Journal, 2005
Photosynthetic bacterial light-harvesting antenna complex LH2 was immobilized on the surface of TiO 2 nanoparticles in the colloidal solution. The LH2/TiO 2 assembly was investigated by the time-resolved spectroscopic methods. The excited-state lifetimes for carotenoid-containing and carotenoidless LH2 have been measured, showing a decrease in the excited-state lifetime of B850 when LH2 was immobilized on TiO 2 . The possibility that the decrease of the LH2 excited-state lifetime being caused by an interfacial electron transfer reaction between B850 and the TiO 2 nanoparticle was precluded experimentally. We proposed that the observed change in the photophysical properties of LH2 when assembled onto TiO 2 nanoparticles is arising from the interfacial-interaction-induced structural deformation of the LH2 complex deviating from an ellipse of less eccentric to a more eccentric ellipse, and the observed phenomenon can be accounted by an elliptical exciton model. Experiment by using photoinactive SiO 2 nanoparticle in place of TiO 2 and core complex LH1 instead of LH2 provide further evidence to the proposed mechanism.